Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, Aurora, CO 80045, USA.
Nucleic Acids Res. 2011 Nov 1;39(20):8820-32. doi: 10.1093/nar/gkr650. Epub 2011 Sep 29.
Metazoan spliced leader (SL) trans-splicing generates mRNAs with an m(2,2,7)G-cap and a common downstream SL RNA sequence. The mechanism for eIF4E binding an m²²⁷G-cap is unknown. Here, we describe the first structure of an eIF4E with an m(2,2,7)G-cap and compare it to the cognate m⁷G-eIF4E complex. These structures and Nuclear Magnetic Resonance (NMR) data indicate that the nematode Ascaris suum eIF4E binds the two different caps in a similar manner except for the loss of a single hydrogen bond on binding the m(2,2,7)G-cap. Nematode and mammalian eIF4E both have a low affinity for m(2,2,7)G-cap compared with the m⁷G-cap. Nematode eIF4E binding to the m⁷G-cap, m(2,2,7)G-cap and the m(2,2,7)G-SL 22-nt RNA leads to distinct eIF4E conformational changes. Additional interactions occur between Ascaris eIF4E and the SL on binding the m(2,2,7)G-SL. We propose interactions between Ascaris eIF4E and the SL impact eIF4G and contribute to translation initiation, whereas these interactions do not occur when only the m(2,2,7)G-cap is present. These data have implications for the contribution of 5'-UTRs in mRNA translation and the function of different eIF4E isoforms.
后生动物拼接的先导（SL）反式拼接生成带有 m(2,2,7)G-帽和常见下游 SL RNA 序列的 mRNA。eIF4E 结合 m²²⁷G-帽的机制尚不清楚。在这里，我们描述了第一个具有 m(2,2,7)G-帽的 eIF4E 结构，并将其与相应的 m⁷G-eIF4E 复合物进行了比较。这些结构和核磁共振（NMR）数据表明，除了在结合 m(2,2,7)G-帽时失去一个氢键外，蛔虫 Ascaris suum eIF4E 以相似的方式结合这两种不同的帽。与 m⁷G-帽相比，线虫和哺乳动物 eIF4E 对 m(2,2,7)G-帽的亲和力都较低。线虫 eIF4E 结合 m⁷G-帽、m(2,2,7)G-帽和 m(2,2,7)G-SL 22-nt RNA 会导致 eIF4E 构象发生明显变化。在结合 m(2,2,7)G-SL 时，Ascaris eIF4E 与 SL 之间还会发生其他相互作用。我们提出 Ascaris eIF4E 与 SL 之间的相互作用影响 eIF4G，并有助于翻译起始，而当仅存在 m(2,2,7)G-帽时，这些相互作用不会发生。这些数据对 5'-UTR 在 mRNA 翻译中的贡献和不同 eIF4E 同工型的功能具有重要意义。
